Ancient sets of teeth discovered by researchers suggest the mammal subgroup that includes charismatic critters like quolls, wallabies and sugar gliders may need to add an extra branch to the family tree.
Australia's marsupials were thought to have descended from a common ancestral lineage that arrived from South America more than 50 million years ago, via Antarctica.
Now, fossils discovered in the Riversleigh World Heritage Area in northwest Queensland indicate more variety among early marsupial fauna.
Lead author of the study published in the Journal of Paleontology, University of New South Wales palaeontologist Tim Churchill, said the three new small, insect-eating species were not closely related to the other marsupials living alongside them.
"Whatever these things were, they seemed to be primitive compared to other marsupials at the time," Dr Churchill said.
The newly-discovered ancient animals had teeth resembling a much older, distinct lineage around for tens of millions of years.
The researchers are proposing a new marsupial order, Keeunamorphia.
"Evolutionary history is a lot more complex than just one group leading to all of Australia's marsupials," Dr Churchill said.
"It's more likely that when Australia was part of Gondwana it was home to a range of primitive marsupial lineages, and that several of them may have contributed to the animals we see today."
Australia is home to more than 200 species of marsupials.
The mammal sub-type are known for developing young in pouches.
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